Universal platform for surface acoustic wave (SAW) based sensors
A universal platform for surface acoustic wave (SAW) based sensors uses a selective sensing film coating on a piezoelectric substrate depending upon the application and the measurand to be measured. A SAW substrate with one or more IDTs and associated microcontroller-based electronics with a power supply can be implemented in the context of a common sensor platform. The platform can be mass produced and a selective coating utilized. The selective coatings can be adapted for use in a sensor involving, for example, gas sensing humidity (metal oxide semiconductors, Polymers, Zeolites), pressure, temperature (metal oxides whose conductivity vary with temperature), force, torque, strain, stress and applications associated with a variety of physical parameters.
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Embodiments are generally related to surface acoustic wave (SAW) based sensors. Embodiments are also related to the field of SAW-based sensors for measuring gas concentration, humidity, strain, pressure, temperature, torque, stress, force, and most of the physical parameters. Embodiments are additionally related to universal platform for surface acoustic wave (SAW) based sensors.
BACKGROUND OF THE INVENTIONAcoustic wave devices have been in commercial use for more than 60 years. The telecommunications industry is the largest consumer, accounting for the use of approximately three billion acoustic wave filters annually, primarily in mobile cell phones and base stations. These components are often provided as surface acoustic wave (SAW) devices, and can act as band pass filters in both the radio frequency and intermediate frequency sections of the transceiver electronics.
Several of the emerging applications for acoustic wave devices as sensors may eventually equal the demand of the telecommunications market. These include automotive applications (e.g., torque, gas concentration and tire pressure sensors), medical applications (e.g., chemical sensors), and industrial and commercial applications (e.g., vapor, humidity, temperature, flow and mass sensors). Acoustic wave sensors are competitively priced, inherently rugged, very sensitive, and intrinsically reliable. Some acoustic wave devices are also capable of being passively and wirelessly interrogated (i.e., no sensor power source required).
Acoustic wave sensors are so named because their detection mechanism constitutes a mechanical or acoustic wave. As the acoustic wave propagates through or on the surface of the material, any changes to the characteristics of the propagation path affect the velocity and/or amplitude of the wave. Changes in velocity can be monitored by measuring the frequency or phase characteristics of the sensor and can then be correlated to the corresponding physical quantity being measured.
An important application of surface acoustic wave (SAW) devices is in the field of physical, chemical and biochemical sensing. Surface acoustic waves are very sensitive to changes in physical properties along the propagation of surface acoustic wave path, which modulates wave parameters such as, for example, propagation time, acoustic impedance, frequency, wave length, etc, including mass loading, conductivity, stress, or the viscosity of liquid. Acoustic wave chemical and biochemical sensors have been popular and successfully used in military and commercial applications. For chemical/biochemical sensing applications, the surface of the delay path (i.e., the piezoelectric member) is generally coated with a chemically selective coating which bonds with the target chemical. This delay line is used in the feedback path of an oscillator circuit.
In one prior art configuration, a sensor chip is provided, upon which at least two surface acoustic wave (SAW) sensing elements are centrally located on a first side (e.g., front side) of the sensor chip. The SAW sensing elements occupy a common area on the first side of the sensor chip. An etched diaphragm is located centrally on the second side (i.e., back side) of the sensor chip opposite to the first side in association with the two SAW sensing elements. Such a configuration thus concentrates the mechanical strain of the sensor system or sensor device in the etched diaphragm, thereby providing high strength, high sensitivity and ease of manufacturing thereof.
In another prior art arrangement, an apparatus can be configured to sense the presence of gases, vapors and liquids using acoustic waves. The apparatus comprises a first part that is configured to generate acoustic waves. The apparatus further comprises a second part having a sensing and acoustic wave guiding device, which is generally configured to sense the presence of such substances and propagate acoustic waves. The first part can be removably fixable to the second part of the apparatus. When the first part is fixed to the second part, the acoustic waves propagate in the second part.
A sensor platform having the capability of multiple measurand operations does not exist. Such a platform, if implemented, could assist in the mass production of the sensors, which reduces the design cycle time and development cost and can be used for multiple measurand. The technical challenge involves implementing a common sensing concept/technique, electronics (i.e., programmable) and a power supply.
The SAW substrate with IDT and associated microcontroller-based electronics with a power supply is a common platform. The selective coating depends on the capability of the measurand to measure. The platform can be mass produced and by experiment for the required measurand and measuring environment, the selective coating is also generally used. The selective coatings are well known for gas sensing humidity (e.g., metal oxide semiconductors, Polymers, Zeolites), pressure, temperature (e.g., metal oxides whose conductivity vary with temperature), force, torque, strain, stress and most of the physical parameters.
BRIEF SUMMARYThe following summary is provided to facilitate an understanding of some of the innovative features unique to the embodiments disclosed and is not intended to be a full description. A full appreciation of the various aspects of the embodiments can be gained by taking the entire specification, claims, drawings, and abstract as a whole.
It is, therefore, one aspect of the present invention to provide for an improved surface acoustic wave (SAW) based sensors.
It is another aspect of the present invention to provide for SAW-based sensors for measuring gas concentration, humidity, strain, pressure, temperature, torque, stress, force, flow (e.g., a platinum heater in the SAW path) and/or a variety of other physical parameters.
It is a further aspect of the present invention to provide for a universal platform for surface acoustic wave (SAW) based sensors.
The aforementioned aspects and other objectives and advantages can now be achieved as described herein. An universal platform for surface acoustic wave (SAW) based sensors uses a selective sensing film coating on a piezoelectric substrate depending upon the application and measurand to measure. The invention uses a SAW substrate with IDT and associated micro controller or/and Digital signal processor (DSP) or/and intelligent smart electronics with a power supply and necessary protections as a common platform. The platform is mass produced and by experiment for the required measurand and measuring environment, the selective coating is used. The selective coatings can be adapted for use in sensors for sensing, for example, gas sensing humidity (e.g., metal oxide semiconductors, Polymers, Zeolites), pressure, temperature (e.g., metal oxides whose conductivity vary with temperature), force, torque, strain, stress and a variety of other physical parameters.
The accompanying figures, in which like reference numerals refer to identical or functionally-similar elements throughout the separate views and which are incorporated in and form a part of the specification, further illustrate the embodiments and, together with the detailed description, serve to explain the embodiments disclosed herein.
The particular values and configurations discussed in these non-limiting examples can be varied and are cited merely to illustrate at least one embodiment and are not intended to limit the scope thereof.
On the other side of the substrate 306, a Pt or similar material heater pattern 303 can be provided for heating the sensing element to maintain a constant temperature and reduce the effect of temperature variation on the sensor performance. The heater element can be composed of platinum or a similarly effective material, which possesses a definite positive or negative temperature co-efficient of resistance so that from a measurement of heater resistance, the temperature can be estimated. The heater constant temperature controller circuit can be provided as a part of a microcontroller or DSP or intelligent/smart electronics, with a provision to enable or disable by a firmware for a specific application.
Acoustic wave devices, such as those depicted in
The power supply system consisting of suitable protection to reverse polarity, over voltage, short circuit and Electromagnetic compatibility 314 supplies power to the sensor system 300. The SAW substrate with IDTs 304, 310 and associated micro controller and/or DSP and/or smart and/or intelligence based electronics with power supply 314 is a common platform. The selective coating or sensing film 308 depends on the measurand to be measured. The platform or system 300 can be mass produced and/or implemented experimentally for the required measurand and measuring environment. In either case (i.e., mass produced or experimental), the selective coating or sensing film 308 is used. The selective coatings or sensing film 308 are well known for gas sensing humidity, pressure, temperature, force, torque, strain, stress and most other physical parameters.
It will be appreciated that variations of the above-disclosed and other features and functions, or alternatives thereof, may be desirably combined into many other different systems or applications. Also that various presently unforeseen or unanticipated alternatives, modifications, variations or improvements therein may be subsequently made by those skilled in the art which are also intended to be encompassed by the following claims.
Claims
1. A universal platform apparatus for a surface acoustic wave (SAW) based sensor, comprising:
- an acoustic wave device for generating an acoustic wave, wherein said acoustic wave device comprises a substrate with at least one input inter digital transducer (IDT) configured along at least one side of said substrate in association with at least one heater element and at least one output inter digital transducer (IDT) and at least one sensing film;
- an input driver for supplying a radio frequency request and a transmitter signal to said at least one input IDT;
- a conditioning circuit for conditioning an output from said at least one output IDT to an output device, thereby providing a universal platform apparatus for SAW-based sensor applications.
2. The apparatus of claim 1 further comprising:
- a temperature sensing and constant temperature controller circuit that measures a resistance of said at least one heater element in order to estimate temperature.
3. The apparatus of claim 1 wherein said substrate comprises a piezoelectric material.
4. The apparatus of claim 1 wherein said substrate comprises a metal insulated material.
5. The apparatus of claim 1 wherein said substrate comprises a ceramic material.
6. The apparatus of claim 5 further comprising a thick piezoelectric material configured above said substrate.
7. The apparatus of claim 5 further comprising a thin film piezoelectric coating configuring above said substrate.
8. The apparatus of claim 1 further comprising a power supply for operating said acoustic wave device and said conditioning circuit.
9. The apparatus of claim 3 wherein said sensing film is selectively coated over said substrate.
10. The apparatus of claim 1 wherein a coating of said sensing film is dependent upon at least one measurand to be measured.
11. The apparatus of claim 1 wherein said at least one heater element comprises platinum.
12. A universal platform apparatus for a surface acoustic wave (SAW) based sensor, comprising:
- a substrate comprising at least one of the following: a piezoelectric material, a metal insulated material or a ceramic material;
- an acoustic wave device for generating an acoustic wave, wherein said acoustic wave device comprises said substrate with at least one input inter digital transducer (IDT) configured along at least one side of said substrate in association with at least one heater element and at least one output inter digital transducer (IDT) and at least one sensing film;
- an input driver for supplying a radio frequency request and a transmitter signal to said at least one input IDT;
- a conditioning circuit for conditioning an output from said at least one output IDT to an output device, thereby providing a universal platform apparatus for SAW-based sensor applications; and
- a temperature sensing and constant temperature controller circuit that measures a resistance of said at least one heater element in order to estimate temperature.
13. The apparatus of claim 12 further comprising a thick piezoelectric material configured above said substrate.
14. The apparatus of claim 12 further comprising a thin film piezoelectric coating configuring above said substrate.
15. The apparatus of claim 12 further comprising a power supply for operating said acoustic wave device and said conditioning circuit.
16. The apparatus of claim 15 wherein said sensing film is selectively coated over said substrate.
17. The apparatus of claim 12 wherein a coating of said sensing film is dependent upon at least one measurand to be measured.
18. The apparatus of claim 12 wherein said at least one heater element comprises platinum.
19. A universal platform apparatus for a surface acoustic wave (SAW) based sensor, comprising:
- a substrate comprising at least one of the following: a piezoelectric material, a metal insulated material or a ceramic material;
- an acoustic wave device for generating an acoustic wave, wherein said acoustic wave device comprises said substrate with at least one input inter digital transducer (IDT) configured along at least one side of said substrate in association with at least one heater element and at least one output inter digital transducer (IDT) and at least one sensing film, wherein said at least one heater element comprises platinum;
- an input driver for supplying a radio frequency request and a transmitter signal to said at least one input IDT;
- a conditioning circuit for conditioning an output from said at least one output IDT to an output device, thereby providing a universal platform apparatus for SAW-based sensor applications;
- a temperature sensing and constant temperature controller circuit that measures a resistance of said at least one heater element in order to estimate temperature; and
- a thin film piezoelectric coating configuring above said substrate.
20. The apparatus of claim 19 further comprising a power supply for operating said acoustic wave device and said conditioning circuit and wherein said sensing film is selectively coated over said substrate.
Type: Application
Filed: Oct 10, 2006
Publication Date: Apr 10, 2008
Applicant:
Inventors: Anil Kumar Ramsesh (Bangalore), Boby Joseph (Bangalore)
Application Number: 11/545,331
International Classification: H03H 9/25 (20060101);